Scanning electron microscopy methods in study of micro objects

Transcription

1 Scanning electron microscopy methods in study of micro objects Project supervisor: dr. Oleg Leonidovich ORELOVICH Students: Ivo Oleg BARDAROV South West University, Bulgaria Ionel Bogdan GUSTER University of Bucharest, Romania Simina Aurelia REBEGEA University Al. I. Cuza of Iasi, Romania Sabina SIMON -University of Bucharest, Romania Tomas VYTISK University of West Bohemia, Czech Republic JINR Summer Student Practice, 1 22 July 2012, Dubna

2 Outlook Introduction Methods and devices Results and discussion Conclusions

3 Introduction Purpose of the project: Learning the physical background behind SEM Getting familiar with the stages of sample investigation when operating a SEM

4 Introduction Scanning electron microscope (SEM) is a device that produces a beam of accelerated electrons used to examine objects on a very fine scale. Compared to the light microscopes, where a system of glass lenses is used in order to bend the light waves and create a magnified image, SEM makes use of electrons and magnetic lenses to form and focus the beam, and then obtain the image. Advantages, compared to the light microscope: Larger depth of field Higher magnification: 10X X Chemical composition and surface morphology Topographic and crystallographic information

5 Introduction Secondary electrons: High intensity of detected signal Topographic characterization of the specimens Low energy (50 ev) Yield: differences in topography with respect to the area tilt. Backscattered electrons High-energy electrons Their yield varies with the specimen's atomic number Z-contrast - higher atomic number appears brighter Characteristic x-rays Elemental analysis

6 Introduction Electron gun: heated W filament Magnetic lens forming and focusing the beam Scanning coils Detectors

7 Methods and devices List of instruments: Specimen holder Conductive materials: silver glue, copper band, carbon disk Ion sputter: JEOL JFC-1100 with Au target SEM: JEOL JSM-840 Auxiliary instruments: tweezers, scissors, hourglass Parameters of ion sputter device: Au (99.99%) target Discharge voltage=1.2 kv Discharge current=10 ma Working pressure=1.2 Torr Deposition time up to 300 s (120 s experiment) Au coating thickness ~ 20 nm

8 Methods and devices Working parameters of SEM: Accelerating voltage: 12 kv Secondary electron energy ~ 50 ev Electron beam current ~ 6e(-11) A Working distance (sample objective lens): mm

9 Methods and devices Preparing the sample: The samples are mounted on the clean specimen stage using silver conductive glue / carbon or copper conducting stickers. Biological samples must be dried in a special manner (prevents shriveling and keeps the shape). Non conductive samples must be coated with a conductive layer (Au in our case) that prevents the target from heating, avoids the charging of the sample (that brings some noise in the SEM image) and increases the secondary emission coefficient for samples (coefficient that is directly proportional to the atomic number of the material). Conductive samples (all metals) -do not require special coating, only mounting on the specimen stage.

10 Results and discussions Polymer membrane with pores.

11 Results and discussions Pore density: 1.12e6 pores/cm2

12 Results and discussions Pore diameter distribution : using ruler (left) mcm 5.5 mcm and using software (right) 5 mcm 6.2 mcm Number of pores Pore diameter (mcm) Pore diameter (mcm) Number of pores

13 Results and discussions The effect of charging of the sample on the SEM image. Coated sample up; not coated sample down; Noise and an unusual contrast and brightness are noticed in the images of the non

14 Results and discussions Tilting the sample holder increases the topography details and the brightness of the surface. Tilt = 0, 15, 30 and 60 ;

15 Results and discussions SEM images of a ball from the tip of a ballpen.

16 Results and discussions Salt crystals Sugar crystals

17 Results and discussions Mosquito parts

18 Results and discussions Pine needle

19 Results and discussions Human hair: Dyed (left) Peroxide blonde (right) Natural female hair (left) Natural male hair (right)

20 Results and discussions Flower details:

21 Conclusions Scanning electron microscope is used for observing and measuring microstructures and nanostructures. While metal samples can be observed as they are, non conductive samples must be coated with a conductive layer. SEM allows the comparison between different types of samples, observe different structures and details. Distorted images might be obtained because of outer magnetic field.

22 Acknowledgements The group would like to thank Dr. Oleg Orelovich for all his time and patience and for his support during our work Thanks to our coordinators for their good advices during the Summer Practice. We would also like to extend our regards to the organizers of the Summer Student Practice and all members of the JINR involved in this project.

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